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\newcommand{\coproduct}{\coprod} \newcommand{\product}{\prod} \newcommand{\closure}{\overline} \newcommand{\integral}{\int} \newcommand{\doubleintegral}{\iint} \newcommand{\tripleintegral}{\iiint} \newcommand{\quadrupleintegral}{\iiiint} \newcommand{\conint}{\oint} \newcommand{\contourintegral}{\oint} \newcommand{\infinity}{\infty} \newcommand{\bottom}{\bot} \newcommand{\minusb}{\boxminus} \newcommand{\plusb}{\boxplus} \newcommand{\timesb}{\boxtimes} \newcommand{\intersection}{\cap} \newcommand{\union}{\cup} \newcommand{\Del}{\nabla} \newcommand{\odash}{\circleddash} \newcommand{\negspace}{\!} \newcommand{\widebar}{\overline} \newcommand{\textsize}{\normalsize} \renewcommand{\scriptsize}{\scriptstyle} \newcommand{\scriptscriptsize}{\scriptscriptstyle} \newcommand{\mathfr}{\mathfrak} \newcommand{\statusline}[2]{#2} \newcommand{\tooltip}[2]{#2} \newcommand{\toggle}[2]{#2} % Theorem Environments \theoremstyle{plain} \newtheorem{theorem}{Theorem} \newtheorem{lemma}{Lemma} \newtheorem{prop}{Proposition} \newtheorem{cor}{Corollary} \newtheorem*{utheorem}{Theorem} \newtheorem*{ulemma}{Lemma} \newtheorem*{uprop}{Proposition} \newtheorem*{ucor}{Corollary} \theoremstyle{definition} \newtheorem{defn}{Definition} \newtheorem{example}{Example} \newtheorem*{udefn}{Definition} \newtheorem*{uexample}{Example} \theoremstyle{remark} \newtheorem{remark}{Remark} \newtheorem{note}{Note} \newtheorem*{uremark}{Remark} \newtheorem*{unote}{Note} %------------------------------------------------------------------- \begin{document} %------------------------------------------------------------------- \section*{rigged limit} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{2category_theory}{}\paragraph*{{2-Category theory}}\label{2category_theory} [[!include 2-category theory - contents]] \hypertarget{rigged_limits}{}\section*{{Rigged limits}}\label{rigged_limits} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{definition}{Definition}\dotfill \pageref*{definition} \linebreak \noindent\hyperlink{characterization}{Characterization}\dotfill \pageref*{characterization} \linebreak \noindent\hyperlink{examples}{Examples}\dotfill \pageref*{examples} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} A \textbf{rigged limit} is a [[2-limit]] which is [[created limit|created]] in 2-categories of algebras and [[lax morphisms|lax]], colax, or pseudo morphisms for a 2-monad. In order to characterize these most precisely, however, it turns out to be convenient to generalize from [[2-categories]] to [[F-categories]], using the corresponding notions of $\mathcal{F}$-monad, $\mathcal{F}$-limit, and so on. \hypertarget{definition}{}\subsection*{{Definition}}\label{definition} Let $D$ be a [[small category|small]] strict $\mathcal{F}$-[[F-category|category]]. Then we have the [[functor category|functor]] $\mathcal{F}$-category $[D,\mathcal{F}]$ (where $\mathcal{F}$ denotes the $\mathcal{F}$-category $\mathcal{F}$). An object of $[D,\mathcal{F}]$ is an $\mathcal{F}$-functor $\Phi\colon D\to \mathcal{F}$, which can be identified with a pair of 2-functors $\Phi_\tau\colon D_\tau \to Cat$ and $\Phi_\lambda\colon D_\lambda\to Cat$ together with a 2-natural transformation \begin{displaymath} \itexarray{D_\tau & & \overset{J_D}{\to} & & D_\lambda\\ & {}_{\Phi_\tau}\searrow & \neArrow & \swarrow_{\Phi_\lambda} \\ & & Cat } \end{displaymath} whose components are full embeddings (objects of $\mathcal{F}$). The [[tight morphisms]] in $[D,\mathcal{F}]$ are $\mathcal{F}$-natural transformations in the usual sense of enriched category theory, whereas its [[loose morphisms]] are 2-natural transformations between loose parts. We also have an $\mathcal{F}$-category $Oplax(D,\mathcal{F})$ with the same objects, whose loose morphisms are [[oplax natural transformations]] between loose parts which are strictly 2-natural on tight morphisms, and whose tight morphisms are those whose components are all tight. The inclusion \begin{displaymath} [D,\mathcal{F}] \to Oplax(D,\mathcal{F}) \end{displaymath} has a left adjoint, which induces an $\mathcal{F}$-[[comonad]] $\mathcal{Q}_c^D$ on $[D,\mathcal{F}]$. \begin{udefn} A weight $\Phi\colon D\to \mathcal{F}$ is \textbf{$l$-rigged} if \begin{enumerate}% \item It is a $\mathcal{Q}_c^D$-coalgebra, and \item The canonical functor $Lan_{J_D} \Phi_\tau \to \Phi_\lambda$ is surjective on objects. \end{enumerate} \end{udefn} We obtain definitions of \textbf{$c$-rigged} and \textbf{$p$-rigged} weights if we replace $Oplax(D,\mathcal{F})$ by $Lax(D,\mathcal{F})$ and $Pseudo(D,\mathcal{F})$, respectively. \hypertarget{characterization}{}\subsection*{{Characterization}}\label{characterization} Let $w$ denote one of $l$, $c$, or $p$. \begin{utheorem} For an $\mathcal{F}$-weight $\Phi$, the following are equivalent. \begin{enumerate}% \item $\Phi$ is $w$-rigged. \item For any $\mathcal{F}$-monad $T$ on an $\mathcal{F}$-category $K$, the $\mathcal{F}$-functor $U_w\colon T Alg_w \to K$ creates $\Phi$-weighted limits. \item For any 2-monad $T$ on a 2-category $K$, the functor $U_w\colon T Alg_w \to K$ (where $K$ denotes the chordate $\mathcal{F}$-category on $K$) creates $\Phi$-weighted limits. \end{enumerate} \end{utheorem} See (\hyperlink{LS}{LS}) for the proof. \hypertarget{examples}{}\subsection*{{Examples}}\label{examples} The following limits are $l$-rigged. \begin{itemize}% \item The [[2-limit]] of any diagram of tight morphisms which is also a limit as a diagram of loose morphisms. This includes any [[product]] and any [[power]]. \item The [[oplax limit]] of any diagram of loose morphisms. \item The [[inserter]] of a [[parallel pair]] $f,g\colon A\to B$ such that $f$ (the domain of the 2-cell to be inserted) is tight. Here the projection to $A$ is tight and tightness-detecting. \item The [[equifier]] of a parallel pair of 2-cells between a parallel pair of 1-morphisms $f,g\colon A\to B$ such that $f$ (the domain of the 2-cells) is tight. Again, the projection to $A$ is tight and tightness-detecting. \item The [[Eilenberg-Moore object]] of a loose monad. Here the canonical forgetful morphism is tight and tightness-detecting. \end{itemize} Each has a fairly obvious dual version which is $c$-rigged. There are $p$-rigged versions as well, but $p$-rigged weights are almost equivalent to [[PIE-limits]]; see (\hyperlink{LS}{LS}) for details. \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item Some limits of diagrams involving both lax and colax morphisms can also be given a $T$-algebra structure; see for instance [[colax/lax comma object]]. \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \begin{itemize}% \item [[Stephen Lack]], ``Limits for lax morphisms''. \emph{Appl. Categ. Structures}, 13(3):189--203, 2005 \item [[Stephen Lack]] and [[Mike Shulman]], ``Enhanced 2-categories and limits for lax morphisms'', \href{http://arxiv.org/abs/1104.2111}{arXiv}. \end{itemize} [[!redirects rigged limit]] [[!redirects rigged limits]] [[!redirects l-rigged limit]] [[!redirects l-rigged limits]] [[!redirects c-rigged limit]] [[!redirects c-rigged limits]] [[!redirects p-rigged limit]] [[!redirects p-rigged limits]] [[!redirects rigged weight]] [[!redirects rigged weights]] \end{document}